Thin-walled, extensible articles such as gloves have been made from natural rubber compositions for a long time. In order to obtain articles having a sufficiently high strength and elasticity from natural rubber compositions, it is necessary to vulcanize or in other ways chemically cross-link the molecular chains of the rubber, which requires the presence of curing agents, activators and/or accelerators. The presence of such agents often gives rise to allergic reactions among the users of the articles. In addition, all latices of natural rubber contain proteins, which in extreme cases may cause allergic reactions e.g. swelling of a person's neck and air passageways. Such allergic reactions can result in fatal cases of anaphylactic shock. Surgeons, health care workers and other persons wearing the gloves are particularly susceptible, but patients are also vulnerable during surgical or other procedures, and the families of all such person can be subjected to airborne particles from clothing, hair or skin. In less extreme cases, other reactions occur, including hand dermatitis and hives.
As a result of the problems with gloves formed from latex-containing materials, efforts have been made to develop thin-walled rubber articles from synthetic polymers. In typical processes, articles made from synthetic polymers are manufactured from styrene block copolymers in a multiple-dip process that involves dipping a mould or former into solutions of the styrene block copolymers and drying the dip-coated mould between each dipping step. Such a process includes the use of starch powder. The powder is applied to the article following the final dip but prior to the stripping of the article from the mould or former. The powder acts to reduce surface tackiness and thus facilitates the donning of the glove.
U.S. Pat. Nos. 3,933,723 and 5,112,900 both relate to the use of solutions containing thermoplastic styrene-tri-block copolymers and plasticizers for the production of thin-walled rubber articles. Such solutions do not contain the proteins present in natural rubber i.e. the solutions are free of latex, and thus thin-walled rubber articles that are hypo-allergenic rubber articles may be obtained.
U.S. Pat. No. 5,444,121 relates to thin-walled rubber articles formed from a variety of compositions of styrene-isoprene-styrene (S-I-S) tri-block copolymers and styrene-butadiene-styrene (S-B-S) tri-block copolymers and, optionally, styrene-olefin-styrene (S-O-S) tri-block copolymers.
U.S. Pat. Nos. 5,112,900 and 5,407,715 describe the use of mixtures of styrene-ethylene/butylene-styrene (S-EB-S) tri-block copolymers in the manufacture of gloves.
Blends of styrene-butadiene block copolymers and styrene-isoprene block copolymers, including S-I-S and S-B-S tri-block copolymers, are disclosed for medical applications, including as gloves, in Canadian 2,112,646. Gloves made from a variety of polymers, including S-I-S and S-B-S tri-block copolymers, without the use of a solvent are disclosed in WO 94/20574.
Common to the solutions disclosed in the above-mentioned patents is the formation of a solid film which is understood to represent a physical cross-linking between the block copolymer molecules present in the solution. When the solvent evaporates, cross-linking is understood to occur between styrene domains of the molecular chains. This cross-linking eliminates the need to use the potential allergy-causing chemicals mentioned earlier. Furthermore, these solutions do not contain the proteins present in natural rubber and it is thus possible by using these solutions to prepare hypo-allergenic rubber articles.
The rubber articles disclosed in U.S. Pat. Nos. 3,933,723; 5,112,900; and 5,444,121 represent progressive developments in physical characteristics, specifically tensile strength and tear resistance. These characteristics are extremely important in providing barrier protection for the user. Unfortunately, the "fit-feel-comfort" qualities of the articles have not been optimized, which often results in premature fatigue, strain and discomfort on the part of the user. This quality is extremely important to rubber articles such as gloves which may be worn by a surgeon for several hours during an operation.
The aforementioned U.S. Pat. No. 5,444,121 reports that articles made from 100 percent styrene-isoprene-styrene (S-I-S) triblock copolymers were thin-walled and sticky, and the use of S-I-S in such rubber articles was limited to no more than 75 percent.